Problem: If $x \bigtriangleup y = xy+2x-y$ and $x \oslash y = 3x+y$, find $(2 \oslash -1) \bigtriangleup 2$.
Solution: First, find $2 \oslash -1$ $ 2 \oslash -1 = (3)(2)-1$ $ \hphantom{2 \oslash -1} = 5$ Now, find $5 \bigtriangleup 2$ $ 5 \bigtriangleup 2 = (5)(2)+(2)(5)-2$ $ \hphantom{5 \bigtriangleup 2} = 18$.